When working with histological samples, in particular when preparing histological samples in the context of an embedding process for later microtoming, it is necessary to be able—in particular between individual process steps that as a rule occur at different laboratory locations and/or in different devices—to grasp the samples and set them down again precisely and gently. One of the difficulties existing in this context is that as a general rule the samples are impregnated or at least wetted with liquids, in particular with liquids that solidify at room temperature (for example, paraffin); this greatly complicates handling with the aid of mechanical grasping tools, for example tweezers. In addition, damage to the sample can occur.
Merely by way of example, mention is made below of a number of process steps during or between which it may be necessary to grasp samples and set them down again: In the context of the conditioning of histological samples, they are usually first fixed by the application of various chemicals. The tissue liquid originally present in the natural cavities of the sample is thereby replaced, in multiple steps, by a fixing liquid, for example by formalin. In order to convert the fixed samples into a state that permits sectioning by means of a microtome, the fixing liquid is replaced by an embedding medium, for example paraffin, gelatin, agar, nitrocellulose, polyester wax, polyethylene glycol, or plastic. During the aforementioned processes, the samples are usually located in a cassette that comprises a plurality of sieve-like openings so that the chemicals can flow around the samples. A particular embodiment of such a cassette is known, for example, from DE 43 33 118 A1. After infiltration of the embedding medium, i.e. for example paraffin, into the samples, the excess embedding medium is drained off. The samples can then be removed from the cassette. After this step, however, the samples can be located anywhere within the cassette; because of the paraffin residues adhering to them, for example, the samples as a rule adhere to the cassette cover, in the cassette cavity, and/or to one another. Stuck-together clumps of samples often form inside the cassette. This complicates reliable, gentle grasping of the individual samples.
Before further processing, in particular before automated, machine-controlled further processing, of the samples, for example before the further step of casting the samples into a paraffin block (called “blocking”), the sample or samples must be present in isolated fashion. Detachment and isolation can be performed, for example, using tweezers; disadvantageously, the risk exists that a sample may be damaged in this context and possibly even become unusable. In particular, the risk exists of unintentionally causing changes to a sample that result in artifacts upon later analysis of tissue sections of the sample.
DE 20 2009 017 635 U1 discloses a grasping apparatus for fixing specimens using a fixing agent. This grasping apparatus comprises a heatable and coolable probe. Also provided is a temperature regulation unit for heating and cooling the probe and for regulating the temperature of the probe in a range, the fixing agent exhibiting in that range a change in aggregate state from solid to liquid. Lastly, the paraffin adhering to a histological sample is used as an adhesion medium that, in the hardened (cooled) state, ensures that the sample to be grasped adheres to the probe. The sample can be detached again from the probe by subsequent heating of the probe, and thus re-liquefaction of the paraffin. In practice, this grasping apparatus is difficult to handle, especially because even liquefied paraffin still exerts an (albeit reduced) adhesive effect between the probe and sample. This, in particular, also disadvantageously prevents the use of this grasping apparatus in an automated system.